14486E38.pdf

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Statistics

Abstract

Our senses are limited in the amount of information they can represent and may overcome this bottleneck by encoding a summary or “gist” of the information rather than the specific details of the stimulus. This “ensemble coding” or summary statistical perception has been widely documented for the visual system, and has recently been found to also hold for sound perception. For example, when a sequence of tones is played, observers are poor at remembering the specific tones while good at recognizing the average tone, even when that average was not present in the set. We examined the nature of this ensemble coding for musical tones, in order to explore how ensemble perception operates across different sound sources (different instruments) and whether it depends on the musical experience of the listeners. Participants were undergraduate students with or without formal musical training. They were presented with a series of four notes (spanning 349.23-554.37 Hz) in random order (600 msec per note separated by 200 msec). The notes came from recordings of a piano or flute, and on different trials were all from the same instrument or from both instruments (one playing solely one instrument and the second alternating between the two). A test note from either instrument was presented 500 msec after the sequence, and the listener reported whether it was part of the sequence. Test notes included the four targets plus five intervening notes at half-step intervals. In preliminary studies, untrained observers confused both the notes and the instruments, consistent with encoding the overall gist of the set. Musicians instead correctly identified the actual notes yet made confusions across the instruments, suggesting that pitch was encoded independently of timbre. These results have implications for understanding how ensemble averaging occurs in music perception and how it is shaped by expertise.